1. Technical Field
This invention relates generally to the optical systems of high energy laser apparatus an more particularly to protection devices for sensing when the potentially damaging radiation breaks free from its designated optical path posing a hazard to the environment outside the optical system.
2. Discussion
High energy lasers have demonstrated utility for many industrial applications. Such laser beams can be used for manufacturing operations ranging from welding automobile body frames to drilling small size holes in metal. The systems are reliable, they can perform with very exacting precision and perform those tasks quite rapidly. As these systems come into greater usage they could pose a hazard to the general working environment in which they are employed unless equipped with appropriate protective devices.
A brief explanation of the construction of the high energy laser system may be helpful in providing a better understanding of the need for protective devices to be incorporated in the apparatus. The high energy laser systems generally comprise a solid state laser source such as a power oscillator that generates a pulse beam, a zig-zag slab gain medium for generating the high power beam. The amplified beam is out-coupled or extracted with a generated beam that ranges from 10 watts to 5,000 watts and greater. The optical path of the beam is such that as it is out-coupled from the laser cavity it is directed onto a series of reflecting surfaces and thereby transmitted to the work site where the beam is to be used. The laser slab that is employed is generally a neodymium YAG ("Nd-YAG") single crystal which is positioned between two reflective surfaces, one which is totally reflective at the front end of the laser slab and at the other end of the laser slab the energy beam is out-coupled through another surface that is partially transmissive and partially reflective. The total reflectivity of the surface at the front end redirects the beam back into the slab and proceeds to zig-zag back and forth between the two reflecting surfaces as it gets properly amplified and is then out-coupled.
It will be understood that the invention is not limited to a particular laser system or geometry. The failure detectors of this invention can be used to advantage with any laser gain medium such as gas, chemical or solid state, equipped with appropriate reflecting mirrors. The light is collimated and amplified by cycling it back and forth through the gain medium.
As long as the high intensity beam remains on the pre-determined optical path from the totally reflecting surface through the out-coupling reflective surface and through the other parts of the optical system until it reaches the work site through a controlled path there is no particular hazard. However, in the circumstance one of the reflective surfaces or other parts of the optical path should experience mechanical failure or for any reason cease to intercept the high power beam, the high energy beam will escape the intended beam path and pose a risk to the environment of the apparatus.
Previous attempts to monitor the conditions in the high energy laser apparatus employed thermal responsive fuse type structures positioned behind the mirrors that melted or fused when heated beyond a threshold temperature. Thermal fuses are bulky and useable only one time. The escape of a 5000 watt beam from its optical path could readily strike through the containing walls of the apparatus and cause damage to property and persons in fractions of a second. The hazards to persons in the vicinity of the apparatus could result in blindness and cause severe burns.
There is a need for detection devices that respond very quickly de-energizing the system thereby minimizing any delay factor between the time mirror failure occurs and the response of any sensing device thereby preventing the beam from escaping from the intended path and is reuseable.